Question

1. Explain the case study where the infant was suffering from LAD. What was the defect, and what were her chances of survival?

2.  Describe the role of interferon, and how it protects us from viral infections. Why doesn't it always work? IN other words, why do we get some viral infections despite having an intact immune system?

3. Why is HIV so devastating to the immune system?

4. How is a DNA virus different from an RNA virus? Give two examples.

Answer 1

1)Leukocyte adhesion deficiency (LAD), is a rare autosomal recessive disorder characterized by immunodeficiency resulting in recurrent infections.It has mainly 3 types LAD1,LAD2 and LAD 3.In case of infants,Type 1 is commonly found.Leukocyte adhesion deficiency type I is an extremely serious and rare form of congenital immunodeficiency with recurrent episodes of infection since neonatal period.Type 1 is characterized by delayed separation of the umbilical cord at birth, persistent leukocytosis and recurring bacterial and fungal infections involving skin, mucosa, impaired pus formation and wound healing.

It is usually diagnosed in childhood, but if diagnosed in early neonatal period then definitive treatment can be instituted early with promising results.The wounds are slow to heal,leading to additional infection. Life expectancy is often severely shortened. Due to repeat infections, affected individuals may not survive past infancy.

2)Interferons belong to large class of proteins known as cytokines, molecules used for communication between cells to trigger the protective defenses of the immune system that help eradicate pathogens.They are named for their ability to "interfere" with viral replication by protecting cells from virus infections.Interferons has other functions like,they activate immune cells, such as natural killer cells and macrophages,they increase host defenses by up-regulating antigen presentation by virtue of increasing the expression of major histocompatibility complex (MHC) antigens. Certain symptoms of infections, such as fever, muscle pain and flu-like symptoms ,are also caused by the production of IFNs and other cytokines.

Many viruses infect humans and most are controlled satisfactorily by the immune system with limited damage to host tissues. Some viruses, however, do cause overt damage to the host, either in isolated cases or as a reaction that commonly occurs after infection. The outcome is influenced by properties of the infecting virus, the circumstances of infection and several factors controlled by the host.

3)HIV (Human immunodeficiency virus) is a virus that cause severe threat to body functioning .It may be transmitted by blood,semen or vaginal fluids.Acute HIV ,Chronic HIV and AIDS are the 3 stages of this disease.

HIV attacks specific type of immune system cell in the body, known as CD4 helper cell or T cell. When this cell is destroyed, it becomes harder for the body to fight off other infections.When HIV is left untreated, even a minor infection like cold can be much more severe. Body will have difficulty responding to new infections.Not only does HIV attack CD4 cells,but it also uses the cells to make more of the virus. HIV destroys CD4 cells by using their replication machinery to create new copies of the virus and finally causes the CD4 cells to swell and burst.During last stages of this disease ,other diseases like TB, pneumonia,cancer can be affected.

4)DNA replication takes place in nucleus while that of RNA take place in cytoplasm.DNA viruses are mostly double-stranded while RNA viruses are single-stranded.RNA mutation rate is higher. DNA viruses are stable while RNA viruses are unstable.RNA viruses skip DNA for duplication and decoding.Examples:-

DNA viruses- Herpesvirus,Papillomavirus,Parvovirus

RNA viruses- Hepatitis virus, HIV